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Slope streaks are a form of down-slope mass movement on the surface of Mars that frequently occurs on Mars today (Image 1 and 2). Slope streaks were first identified on high-resolution Viking Orbiter images, but their present-day activity was only discovered in Mars Orbiter Camera (MOC) images.

Image 1. A portion of a Mars Orbiter Camera image taken on 1999-10-28.

Image 2: An Image of the same area taken on 2002-06-10. A large new slope streak formed, while numerous other streaks persisted. North is up and illumination is from the lower left (Schorghofer et al. 2007).

The High Resolution Imaging Science Experiment (HiRISE) onboard Mars Reconnaissance Orbiter (MRO) has imaged the Martian surface for two full Earth years at spatial scales up to 25 centimeters/pixel. These images allow very detailed studies of small surface features, such as slope streaks, commonly seen in the high albedo, low thermal inertia, and dust-rich equatorial regions of Mars. Slope streaks have been observed in all spacecraft images from the early Mariner missions to the most recent Mars Reconnaissance Orbiter (MRO) mission to Mars [1-8]. Recently formed slope streaks are typically darker than their surroundings and appear to fade (i.e., brighten) over time (Image 1). Typical characteristics of slope streaks are initiation at a point source, one streak splitting into two, deflection around or over obstacles such as small boulders or crater rims, widening below the source area up to a few hundred meters, and lengths of up to a few kilometers. Numerous models have been proposed for their formation, both dry- and wet-based, and these are described briefly in [6].

Image 1: Portion of HiRISE image PSP_003259_1850 (5.0 N, 32.7 E) near Naktong Vallis with dark slope streaks along the interior slope of an impact crater. Arrows point to the margin of slope streaks that have topographic relief where the streaked surface is lower than the surrounding un-streaked surface. Several of the streaks are triggered by impact craters that have dark ejecta. Image credit: HiRISE (NASA/JPL/Univ. of Arizona)